The development and progression of various forms of arthritis is being investigated in American Indian populations. The patterns of joint disease will be examined to determine if distinctive patterns of degenerative joint disease can be recognized, and the prognostic significance of various factors related to rheumatoid arthritis and ankylosing spondylitis determined. The study which includes clinical radiographic and serologic studies of joint disease is a part of a prospective study of the Gila River Indian Community where studies of diabetes mellitus and other diseases are also being undertaken. The frequency of Reiters Disease and ankylosing spondylitis and their relationship to HLA, and the possible role of infection in producing these disorders in Navaho and Hopi Indians have been investigated.